feat(ingest): end-to-end idempotent ingest pipeline
Implements codex/ingest.py with:
- OpenAlex primary / Semantic Scholar fallback metadata fetch
- Abstract dense embedding (zero-vector for missing abstracts)
- Idempotent paper upsert (ON CONFLICT DO UPDATE)
- Source file parsing (.tex via latex_to_text, .pdf via nougat + grobid)
- Chunk deletion + bulk re-insert with dense embeddings
- Citation merge from OpenAlex/S2 API and GROBID PDF refs (dedup via set)
- 7 tests covering basic, tex, pdf, not-found, idempotent, arxiv-fallback,
and no-abstract scenarios (all mocked, offline)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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